Method of treating rare earth ores



United States Patent 2,735,747 METHOD OF TREATING RARE EARTH ORES John Bryant Kasey, Bakersfield, Calif.

N 0 Drawing. Application April 30, 1952, Serial No. 285,319

15 Claims. (Cl. 2316) The present invention relates to the treatment of ores containing rare earth minerals and particularly lanthanum minerals, but which may also include rare earth elements such as praseodymium, erbium, neodymium, samarium, cerium; some of the rare earth elements, of the yttria group; and thorium. More particularly, the present invention relates to the treatment of rare earth minerals, including lanthanum minerals, which are amenable to heat treatment to convert the rare earth minerals of low specific gravity into rare earth minerals or compounds of high specific gravity whereby the latter are then amenable to gravity separation from the valueless gangue components of the ore.

The present invention is particularly applicable to ores containing rare earth minerals having as gangue components alkaline earth metal compounds as, for example, calcite, barite (barium sulphate), and witherite (barium carbonate). However, the ores which are treated in accordance with the present invention may contain other gangue components. The invention is particularly ap plicable to the treatment of rare earth carbonates and particularly lanthanum carbonate.

Rare earth carbonates, flue-carbonates, and fluorides frequently occur in a predominating calcite or calcitebarite-witherite gangue. However, the recovery of the rare earth carbonates has not been possible prior to the present invention because of the similar chemical and physical properties of the rare earth carbonates and the gangue minerals associated therewith, including specific gravity of the rare earth carbonates and particularly lanthanum carbonate. Attempts have been made to separate the desirable rare earth carbonates from the gangue associated therewith by chemical flotation or gravity methods of separation based on specific gravity differences, and the results prior to the present invention have been negative.

One object of the present invention is to convert rare earth carbonates into other chemical compounds and more particularly, into oxides, the latter having a greater density than any of the gangue minerals present in the ore.

Another object of the present invention is to convert the rare earth carbonates, including lanthanum carbonate, by heat treatment into oxides of high specific gravity and usually a specific gravity of between 6 and 7 so that there is a gravity differential between the so-produced rare earth oxides and the gangue components associated therewith so as to enable the separation of the valuable rare earth minerals and the valueless gangue components by any of the prior art methods of separation, including flotation processes and gravity processes.

It has been discovered that by subjecting divided or crushed raw rare earth ores of the character herein set forth to a temperature between the decomposition temperature of the rare earth minerals, including lanthanum carbonate, and below the temperature at which incipient fusion of the ore occurs, that the rare earth minerals and certain of the gangue components are converted into oxides, the gravity of the converted rare earth oxides being greater than that of separation from each other.

More specifically, it has been discovered that when the divided ore of the present invention is subjected to a temperature of above 1000 C., all of the carbonates of the rare earths and lanthanum are decomposed. The carbon dioxide and the water of composition, if any, such as in lanthanite Laz(COs)s-9Hz0, are driven off, leaving the lower oxides of the rare earths. Since when an oxidizing atmosphere is maintained during the heating process, oxygen is present in the air surrounding each particle of ore, the lower or sesquioxides, especially those of cerium, praseodymium, and erbium, are oxidized to higher oxides or peroxides, the mass of oxides usually becoming rusty red on cooling. Where it is desired to prevent the formation of peroxides of the rare earth minerals herein set forth, this can be prevented by maintaining within the treatment vessel an inert or reducing atmosphere. During the heating step the calcite and witherite present are decomposed at temperatures above 1000 C into their respective oxides.

it is desired to point out that the ore must be heated to a temperature of or above the decomposition temperature of the rare earth minerals, including lanthanum carbonate. For example, when an ore containing rare earth minerals including lanthanum carbonates and having present over 35% of volatile matter such as carbon dioxide and water, was heated to between 850 and 900 C. for two hours, there was a loss of 39% of the total carbon dioxide and water present. However, when a portion of the so-processed ore was treated with dilute hydrochloric acid, a vigorous effervescence resulted due to carbon dioxide being evolved from the burnt ore. When a specimen of the same ore which had been heated to 1000 C. for the same period of time was treated with dilute hydrochloric acid and tested as before, the heattreated ore gave no effervescence of carbon dioxide. This test shows that the lanthanum carbonate is not decomposed at the lower temperature, whereas calcite is, and

that a higher temperature, namely, a temperature over 1000 C. is necessary to convert the rare earth mineral compounds, including lanthanum carbonate, into oxides having a gravity or density greater than the gravity or density or" the gangue oxides.

Proceeding as set forth, two important results are obtained: first, the rare earth and lanthanum mineral carbonates are transformed from compounds of low specific gravity to compounds of high specific gravity. More particularly, lanthanite having a specific gravity of 2.6 and having chemical properties more or less similar to those of the carbonate gangue, is converted to an oxide or oxides with a gravity over 6.5, and whose chemical properties are much unlike the simultaneously and newlyformed oxides of certain of the gangue components and more particularly, oxides of calcium and barium. The second beneficial result that is obtained by practicing the present invention is that the cohesion between the crystalline particles of the several minerals of the divided ore is completely and effectively destroyed. Preferably, although not necessarily, the ore is crushed to a rather coarse state to most satisfactorily effect this result, the size varying preferably between about A" or /2 to about 2" or 2%". While, as stated, it is desirable to have the ore coarsely crushed, the ore may be divided from an exceedingly fine size to a very coarse state. The coarse crushing is preferred because when the ore is coarsely crushed, excessive dusting losses are avoided as would occur when the product is continuously fed into a kiln for the oxidizing or reducing heat treatment or calcination. Further, it costs less to crushed ore.

prepare the coarsely severalminerals; including the-valuable components and the valueless gangue, is so well destroyed that subsequent pulping of the heat-treated ore with water slakes theore to an exceedingly fine condition as, for example, to a molecularly-fine condition, liberating substantially all of the. particles of usefulmineral andinert gangue, such as barite which is barium sulphate, which may occur in irregular and large pieces. The destruction of the cohesiveness between the. crystalline particles of the several minerals liberates the rare, earthmineral particles, including lanthanum carbonate, almost in their original stateof size,,and since no abrading force is applied, as is truewhen an ore isground, there is a minimum of sliming of the valuable. rare earth minerals, including lanthanum carbonate.

Since the heating following the crushing step as herein set forth destroys the cohesion between the individually mixedminerals. in the ore, as stated, coarse grinding is more economical. and further the heating cycle liberates substantially each individual mineral practically free of its neighboring gangue to thereby. facilitate the transformation of the'carbonates of the herein set forth rare earth elements into oxides.

While the gangue of the ore may contain calcite, which is a carbonate, and witherite, which is a carbonate, both of which are capable of being transformed into oxides upon heat treatment at the temperatures herein set forth and at temperatures below about 1000 C., the gangue of the ore being treated in accordance with the present invention may contain other gangue components. Further, some of the rare earth carbonates may have a fluorine replacement atom so that the carbonate becomes a fluo-carbonate. For example, there may be present bastnasite, which is also known as hamartite having the formula [(Ce, La, Di)F]CO3. Bastnasite is an acid insoluble compound forming hexagonal crystals. Barite may also be present in the ore and directly attached to such fluorides with no intervening calcite cementing m..- terial. Under these circumstances, the liberation of valuable rare earth minerals, including lanthanum carbonate, with comparatively valueless barite gangue, can be effected only by physically crushing the mixture to cause liberation of the valuable rare earth minerals.

There may also be present a certain amount of quartz together with barite. In one form of the invention, the barite gangue and any quartz may be screened out at a suitable mesh and deslimed in water cones, or classified. If coarse'rare earth minerals, such as the fluorides, are present in the deslimed coarse product, then grinding is desirable and almost necessary for this portion ofthe ore to secure separation of the remaining rare earth from the gangue. However, the heat treatment herein referred to obviates the necessity of fine grinding of all of the ore to secure satisfactory liberation of the valuable rare earth minerals from the gangue and in many cases it is not necessary to preliminarily remove any of the gangue components prior to theheat treatment. Obviously, the elimination of the removal of the gangue components prior to heat treatment is an economic advantage of considerable importance. Upon slaking the heat-treated ore, the resulting pulped slaked product is in a fine state and is further diluted with water to form' a dilute suspension containing 5 to 10% of solids. During pulping the calciunrand bariumoxides hydrate but the heavy rare earth and lanthanurnoxides donot hydrate and, therefore, the slaked pulped'product may be subjected to a concentrating operation to effect a separation of the gangue components including the calcium and barium oxides, from the rare earth and lanthanum oxides. This separation may be effected on concentrating'tables or by flotation processor by any other suitable gravity device. It may be stated that'the marked increase in specific gravity of the rare earths including lanthanum compounds when they are transformed into oxides over that of the calcium and barium hydrates is so great that the latter arevery'easily'and completelywashedaway from the valuable rare earth oxides, including the lanthanum oxides. Barite, which has a specific gravity of 4.6, if it has not been reduced to a slakeable state, is concentrated with the lanthanum and rare earth oxides and fluorides. However, the barite may be removed if strong reducing conditions are maintained during the heat treatment as by the presence of lcarbon to therebyconvertthe sulphate of barium into the sulphide which. is subsequently hydratcd upon theslaking of the heat-treatedore and is slimed along with the; calcium and barium hydrates, since the specific gravity oftthe' sulphide' is below 3.0.

The heat-treated. ore. is. slakcd and transformed into a dilute suspension in order to avoid any mechanical entrainment of valuable minerals with the gangue going into the tails and any substantial entrainment of the gangue in the valuable concentrate. The range herein set forth of a dilute solution containing about 5% to 10% of solids is a safe. range. Higher than 10% will,

cause losses in the tails and dilution ofthe concentrates. While the. 5% to 10% range is. somewhat critical,.it is desired to point out that this may vary somewhat for different ores and'it is not desired to be limited strictly to said percentages. The better statement of the problem is that the dilution of the suspension shouldbe. such that there is obtained a clean gangue containingrelatively little concentrates and a cleanv concentrate containingvery little gangue, and'this is the criterion for the dilution.

The following .is an example of a calciferous ore which may be treated in accordance with the present invention, it being pointedout thatthe ore contains rare earth oxides which are designated as REO, said rare earth oxides also containing lanthanum as one. of the associated elements of the rare earth group. However, lanthanum also occurs in the particularore treated as a free carbonate, free of the other rare earth elements. If any flue-carbonates, such as bastnasite, are present, they areincluded in the REO analysis.

Raw ore Percent REO andbarite- 21.30 FezOa, etc. 3.39 1.21203 27.50 CaO 12.05 CO2 andHzO 35.52

Two pounds of theme havingan analysis such as above set forth is reduced to a' size between the limits of about /2 to 2" indiameter and placed in an electrically-heated mutfie furnace in which air freely circulates .and which-is maintained at a'temperature' of 1,000 to-l,200 C.' This maintains the-ore at a temperature at or above the decomposition temperature of the rare earth-minerals, including lanthanum carbonate; and below the temperature'wherein incipient fusion of the ore components occurs. The ore is kept at a temperature between the range above set forth until the rare earthminerals and certain of the gangue components which are capable of being converted by heat treatment to oxides, areconverted into oxides. Illustratively, the ore is kept'within the temperature range'set' forth for threehours and is then withdrawn and cooled to preferably roorn' temperature-which may be taken as between the limits of 25 C. and 60' C. or'evcn higher, before water is added thereto. In the alternative, the soheat-treated ore may be plunged directly into water tofurther disintegrate the ore. Incommercial work the latter procedure is the better one. In most of the experimental work conducted inconnection with the presentinvention; the ore was cooled-to room temperature before subjecting it to the hydratingaction ofwater as'a great deal of-heat'is evolved'as-a result of 'theh'ydrating action. Inactual practice thehot calcined' ore may-be desirably dropped from the discharge end of the kiln directly into the water, excessive explosive generation of steam being avoided. The object of the hydration step is to disintegrate the calcine as the calcium oxide hydrates and liberates changed and unchanged mineral constituents for subsequent gravity separation.

The heat-treated ore was cooled prior to being slaked and it was found that the heat residue weighed only 20.7 ounces, showing a loss of 11.3 ounces, due to the evolution of carbon dioxide and water of composition. The loss of carbon dioxide and water is actually a small amount greater than that set forth, but this loss is compensated for by the absorption of oxygen to form peroxides, especially by cerium, praseodymium, and erbium sesquioxides. This loss, of course, will be diiferent in different ores in accordance with the percentage of decomposable rare earth carbonates present originally in the ore being treated.

The color of the cooled burnt or calcined ore is a mottle of white patches and dirty-red due to brown to black oxides of iron and manganese and the rusty-red rare earth oxides. The cooled mass of 20.7 ounces of heat-treated calcined ore is immersed in one part of water to slake the ore. The slaking rapidly occurs with evolution of a great deal of heat because of the avidity with which the calcium and barium oxides react with the water to form calcium and barium hydrates. As soon as slaking is complete, more water is added so that the resulting pulp is diluted to a point which insures fairly clean concentrate and fairly clean tails upon concentration of the pulp, satisfactory results being obtained when the suspension of thepulp contained between and solids. Thereafter, the dilute pulp is fed to a small concentrating table and the light barium and other light gangue present, washed into the tailings. The dense and very heavy rare earth and lanthanum oxides are obtained as a mixed concentrate with the unchanged rare earth fluorides and barite.

The following table sets forth a comparison of the analysis of the raw ore, the burnt ore, ar calcined ore, the tabling concentrate, and the tabling tails.

Since lanthanum occurs in the ore in two forms, as free carbonate and as one of the naturally associated elements of the rare earth group, the amounts of each of these components are separately set forth. The raw ore contained 48.80% of rare earth oxides and barite, and lanthanum oxide La203; the burnt ore contained 76.60% of these constituents, and the concentrate contained 92.90% of these constituents. This illustrates exceedingly well how the ore is concentrated to provide a high grade concentrate of the rare earth oxides, barite, and lanthanum oxide. By heating to 1000" C. and driving oif the CO2 and water of composition, the combined rare earth oxides and barite are increased from 21.30 to 33.48, which is an increase of 57%. By concentrating on tables, the slaked burnt ore, the rare earth oxides and barite are increased from 21.30% to 41.90%, or an increase of 20.60% which is well over a 90% increase. The ore also contained free lanthanum carbonate which is broken down in the rare earth ore analysis to a lanthanum oxide content of 27.5. Of course, in the raw ore the oxide was not actually present but it is indicated in the broken-down analysis. The lanthanum carbonate present in the raw ore and expressed as LazOs, increased from 27.50 to 43.12 in the burnt 6 calcined ore and the tabling concentrate contained 51% of LazOs.

While the invention has been described in connection with the processing of a fairly rich calciferous ore, the invention is applicable to other ores including lean calciferous ores, and applicable to any ore which contains lanthanum carbonate either as a combined carbonate or as a free carbonate, or in both states.

In carrying out the present invention, during the heat treatment step it is preferable to form rare earth oxides rather than peroxides, since the rare earth oxides are higher in gravity than the peroxides and they are more soluble in acids. Non-peroxide formation may be determined from the fact that chlorine is not evolved when the cooled oxide is dissolved in strong hydrochloric acid.

By the term rare earth oxides is meant the oxides of the rare earth metals of the ceria group and of the yttria group. The ceria group includes cerium, lanthanum, neodymium and praseodymium (previously termed didymium), samarium, europium, and illinium. The classification of the rare earth metals of the ceria group and the rare earth metals of the yttria group are set forth on pages 722 and 723 of Hackhs Chemical Dictionary, Grant, 3d edition, 1944, The Blakiston Company, Philadelphia.

The present invention also resides in the production of a calcined mixture of rare earth mineral oxides including lanthanum oxides and oxide gangue components capable of being slaked with water, said rare earth minerals having a specific gravity greater than that of the oxide gangue components. The principal oxide gangue components are calcium oxide and barium oxide.

What is claimed is:

1. The method of treating ore containing valuable rare earth carbonates including lanthanum carbonate and a valueless gangue component, at least a part of the gangue component also being in the form of a carbonate which decomposes at a temperature below that of the rare earth carbonates, comprising heating the ore in a divided state to a temperature between the decomposition temperature of said rare earth carbonates and a temperature below where incipient fusion of the ore occurs, said gangue carbonate component also simultaneously decomposing during said heating step, to thereby convert the rare earth carbonates including lanthanum carbonate and said carbonate gangue component into the oxide form, the specific gravity of the converted rare earth oxides being greater than the specific gravity of the original rare earth carbonates and greater than the specific gravity of the gangue oxide-component, whereby said mixture of oxides is amenable to gravity separation, and recovering the valuable rare earth oxides from the mixture of oxides by gravity separation.

2. The method defined in claim 1 wherein the heating is effected under oxidizing conditions.

3. The method defined in claim 1 wherein the heating is effected under reducing conditions.

4. The method defined in claim 1 in which the ore is crushed prior to heat treatment to a size between the limits of about A and about 2 /2" to 3".

5. The method of treating ore containing valuable rare earth carbonates including lanthanum carbonate and a valueless gangue component, at least a part of the gangue component also being in the form of a carbonate which decomposes at a temperature below that of the rare earth carbonates and capable of being transformed by heating into a material slakeable in water, comprising heating the ore in a divided state to a temperature between the decomposition temperature of said rare earth carbonates and a temperature below where incipient fusion of the ore occurs, said gangue carbonate component also simultaneously decomposing during said heating step, to thereby convert the rare earth carbonates including lanthanum carbonate and said carbonate gangue component into the oxideform, the specific gravity of the converted rare earth oxides being greater than the specific gravity of the original rare earth carbonates and greater than the specific. gravityof the gangue-oxide-component, slaking said mixture of oxideswith-water to convertthe slakeable oxide'material into-a-hydrate of 10wv specific gravity while the: rare earth: oxides including lanthanumoxide ofv high specific gravity remains unchanged, subjecting saidmixture of oxides of highanddow specific gravity-to a wet gravity separation step,,and recovering the valuable rare oxidesfromthe mixture. of oxides.

6. Themethod oftreating ore containing valuable rare earth-carbonatesincludinglanthanum carbonate and a valueless-gangue component, at-least apart of the gangue component alsobeing in the form of acarbonate which decomposesat atemperature belowthat of-the rare earth carbonatesand capable of beingtransformedbyheating into a material slakeable in'water, comprising heating the oreein-a divided state to'atemperaturebetween the decomposition temperature of said rare earth carbonates and a temperature belowwhererincipient fusion of the ore occurs, said gangue carbonate componentalso simultaneously -decompesing during said heating step, to thereby convert the rare earth carbonates including lanthanum carbonate and said'carbonate gangue component into the oxide form, the specific gravity of the converted rare earth oxides being. greater than the specific gravity of the original'rare earthcarbonatesand greater than the specifie gravity of the gangue oxide-component, whereby said mixture of oxides is amenable to gravity separation, aqueously slaking the so-treated ore'and forming a dilute suspension of the valuable oxides to avoidon concentration entrainment of the valuable oxides with the, gangue component constituting the tails, and recovering from said suspension by concentration in water a heavy mixed rare earth oxide concentrate including lanthanum oxide.

7. The method of treating ore containing valuable rare earthcarbonates including lanthanum-carbonate and a valuelessgangue component, at least apart of the gangue component also being in the form of a carbonate which decomposes at a temperature belowthat of the rare'earth carbonates and capable of being'transformed by heating into a-material slakeable inwater, comprising heating the ore in a dividedstate to a temperature betweentabout 1000 C. and about 1200 C. to thereby; convert'therare earth carbonates including lanth'anumcarbonate and said carbonate gangue component into theoxide form,. the specific gravity of the converted rare earth oxides being greater than the specific gravity of the original'rare earth carbonates and greater than the specific gravity of the gangue oxide-component, whereby said mixture of oxides isamenable to gravity, aqueously slaking the so-treated ore and forming a dilute suspension of the valuable oxides to avoid on concentration entrainment-of the valuable oxides with the gangue component constituting the tails, and recovering from said'suspension by concentration in water'a heavy mixed rare earth oxide concentrate including lanthanum oxide.

8. The method of treating ore containing valuable rare earth carbonates-including lanthanum carbonate and a valueless gangue component, at least-a part of the gangue component-also being in the form of a carbonate which decomposes at a temperature below that of the rare earth carbonates and capable of being transformed by heating into a material slalteable in water, comprising heating the ore in a divided state to a temperature between the decomposition temperature of said rare earth carbonates and a temperature below where incipient fusion of the ore occurs, said gangue carbonate componentalso simultaneously decomposing during said heating step, to thereby convert the rare earth carbonates including lanthanum carbonate and said carbonate gangue component'into the oxide. form, the specific gravity of the converted rare earth oxides being: greater than the specific gravity of the original-rare earth carbonates and-greater than the-specificgravity of the gangue oxide-component, whereby said iii) mixture of oxides is amenable to gravity separation, aqueously slaking the so-treated ore and forming a dilute suspension containing between 5' and 10% of solids to avoid on concentration entrainment of the-valuable oxides with the gangue component constituting the-tails, and recovering from said suspension by concentration in water a-heavy mixed rare oxide concentrate including lanthanum oxide;

9. The method of treating ore containing valuable rare earth carbonates includinglanthanum carbonate and a valueless gangue component, at leastia part of the gangue component including calcium and barium carbonates which decomposes in the presence of said rare earth compounds at a temperature below-that ofthe rare earth compounds, said carbonates beingcapable of being transformed byheating into compounds slakeable in water, comprising heating the ore-ina-divided stateto a temperature between the decomposition temperature of said rare earth carbonates and a-temperature below where incipient fusion ofthe oreoccurs, the calcium and barium carbonates also simultaneously decomposing during said heating step, to thereby convert'the rare earth carbonates including lanthanum carbonate and the calcium'and barium carbonates into the oxide form, the'specific gravity of the converted rare earth oxides'being greater than the specific gravity of the original rare earth carbonates and greater'than-the specific gravity of the calcium and barium-oxides'wherebysaid mixture of oxides-is amenable to gravity separation, slaking-said-mixture of oxides withwater to convert the slakeable calcium and barium oxides into hydrates of low specific gravity while the rare earth oxides-including lanthanum oxide of high specific gravity remains unchanged, subjecting said-mixture of oxidesofi. high and low specific gravity to a wet gravity separation step, and-recovering the valuable rare earth oxides from the mixture of oxides.

10. The method of treating ore containing valuable rare earth carbonates including lanthanum carbonate and a valuelessgangue component, at least a part of the gangue component including-calcium and barium carbonates which decomposes in the presence of said rare earth compounds at a temperature below that of the rare earth compounds, saidcarbonates being capable of being transformed by heating into compounds slakeable in water, comprising heating the ore in a divided state to a temperature between the decomposition temperature of said rare earth carbonates and a temperature below where'incipient fusion or. the ore occurs, said gangue carbonate component of said calcium and barium carbonates also simultaneously decomposing duringthe said'heating step, to thereby convert the rare earth carbonates including lanthanum carbonate and the calcium and barium carbonates into the oxide form, the specific gravity of theconverted rare earth oxides being greater than the specific gravity of the original rare earth'carbonates' and greater than'the specific gravity of'the calcium and barium oxides whereby said mixture of oxides is amenable to'gravity separation, aqueously slaking the so-treated ore and forming a dilute suspension containing hydrated calcium and barium compounds and valuable rare earth'oxides, said diluted suspension-avoiding entrainment of the valuable oxides with the gangue component constituting the tails, feeding ing in the presence of said rare earth oxides at a temperature below the decomposition temperature of the rare earth oxides, said calcite being capable of being transformed into a state slakeable in water, comprising heating the ore in a divided state to a temperature between the decomposition temperature of said rare earth carbonates and a temperature below where incipient fusion of the ore occurs, said calcite simultaneously decomposing during said heating step, to thereby convert the rare earth carbonates including the lanthanum carbonate and the calcite into the oxide form, the specific gravity of the converted rare earth oxides being greater than the specific gravity of the original rare earth carbonates and greater than the specific gravity of the gangue oxide component including calcium oxide produced during said heating step, whereby said mixture of oxides and barite is amenable to gravity separation, converting the gangue oxide component into a hydrate state of low specific gravity while the rare earth oxides of high specific gravity remain unchanged, and recovering by gravity separation the valuable rare earth oxides in admixture with barite from the mixture of oxides and barite.

13. The method of treating ore containing valuable rare earth carbonates including lanthanum carbonate and a valueless gangue component, at least a part of the gangue component being calcite and barite, the calcite decomposing in the presence of said rare earth oxides at a temperature below the decomposition temperature of the rare earth oxides, said calcite being capable of being transformed into a state slakeable in water, comprising heating the ore in a divided state to a temperature between about 1000 C. and about 1200 C., to thereby convert the rare earth carbonates including the lanthanum carbonate and the calcite into an oxide form, the specific gravity of the converted rare earth oxides being greater than the specific gravity of the original rare earth carbonates and greater than the specific gravity of the gangue oxide component including the calcium oxide produced during said heating step, whereby said mixture of oxides and barite is amenable to gravity separation, aqueously slaking in water the resulting mass to further increase the specific gravity difierential between the rare earth oxides including lanthanum oxide and calcium oxide, the latter being hydrated during the slaking and the rare earth oxides and the barite remaining unslaked, and recovering by gravity separation the valuable rare earth oxides lanthanum oxide in admixture with barite from ture of oxides and barite.

including the mix- 14. The method defined in claim 13 in which the ore is crushed prior to heat treatment to a size between the limits of about A and about 2% to 3".

15. The method of treating ore containing valuable rare earth carbonates including lanthanum carbonate and a valueless gangue component, at least a part of the gangue component being calcite decomposing in the presence of said rare earth oxides at a temperature below the decomposition temperature of the rare earth oxides, said calcite capable of being transformed by heating into a state slakeable in water, and barite, comprising heating the ore in a divided state in a reducing atmosphere to a temperature between the decomposition temperature of said rare earth carbonates and a temperature below where incipient fusion of the ore occurs and converting the rare earth carbonates including the lanthanum carbonate into an oxide form, the calcite being converted into slakeable calcium oxide and the barite by reduction being converted into a sulfide capable of being hydrated upon slaking, the specific gravity of the converted rare earth oxides being greater than the specific gravity of the original rare earth carbonates and greater than the specific gravity of the calcium oxide and the barium sulfide whereby said mixture of oxides and barium sulfide is amenable to gravity separation, aqueously slaking in water the resulting mass to hydrate the calcium and barium compounds of low specific gravity while the rare earth oxides including lanthanum oxide of high specific gravity remain unchanged, subjecting the mixture to a wet gravity separation, and recovering therefrom the rare earth oxides including lanthanum oxide.

References Cited in the file of this patent UNITED STATES PATENTS 1,429,550 Vogt Sept. 19, 1922 1,487,806 Rasor Mar. 25, 1924 1,546,854 Miller July 21, 1925 1,554,917 Kunkle Sept. 22, 1925 1,927,726 Weil Sept. 19, 1933 2,000,656 Armstrong May 7, 1935 2,394,362 Burwell Feb. 5, 1946 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, published by Longmans, Green and Co., New York, 1924, vol. 5, pages 664 and 665. 

1. THE METHOD OF TREATING ORE CONTAINING VALUABLE RARE EARTH CARBONATES INCLUDING LANTHANUM CARBONATE AND A VALUELES GANGUE COMPONENT, AT LEAST A PART OF THE GANGUE COMPONENT ALSO BEING IN THE FORM OF A CARBONATE WHICH DECOMPOSES AT A TEMPERATURE BELOW THAT OF THE RARE EARTH CARBONATES, COMPRISING HEATING THE ORE IN A DIVIDED STATE TO A TEMPERATURE BETWEEN THE DECOMPOSITION TEMPERATURE OF SAID RARE EARTH CARBONATES AND A TEMPERTURE BELOW WHERE INCIPIENT FUSION OF THE ORE OCCURS, SAID GANGUE CARBONATE COMPONENT ALSO SIMULTANMEOUSLY DECOMPOSING DURING SAID HEATING STEP, TO THEREBY CONVERT THE RARE EARTH CARBONATES INCLUDING LANTHANUM CARBONATE AND SAID CARBONATE GANGUE COMPONENET INTO THE OXIDE FORM, THE SPECIFIC GRAVITY OF THE CONVERTED RARE EARTH OXIDES BEING GREATER THAN THE SPECIFIC GRAVITY OF THE ORIGINAL RARE EARTH CARBONATES AND GREATER THAN THE SPECIFIC GRAVITY OF THE GANGUE OXIDE-COMPONENT, WHEREBY SAID MIXTURE OF OXIDES IS AMENABLE TO GRAVITY SEPARATION, AND RECOVERING THE VALUABLE RARE EARTH OXIDES FROM THE MIXTURE OF OXIDES BY GRAVITY SEPARATION. 